1. Field of the Invention
This invention relates to a breaker device having an incomplete-connection prevention function.
The present application is based on Japanese Application Nos. Hei. 9-239952 and 9-285499, which are incorporated herein by reference.
2. Description of the Related Art
FIGS. 1 and 2 show one known breaker device having an incomplete-connection prevention function. This breaker device comprises a pair of fixed electrodes 2 and 3, a moving electrode 4, a lever 5, a torsion coil spring 6, and a lock portion 7. The pair of fixed electrodes 2 and 3 is provided in a housing 1, and the two electrodes 2 and 3 are in opposing relation to each other. The moving electrode 4 is slidable between a position where it connects the two fixed electrodes 2 and 3 together and a position where it disconnects the two fixed electrodes from each other. The lever 5 is tiltably supported on the housing 1, and is connected to the moving electrode 4. The torsion coil spring 6 urges the lever 5 in a disconnecting direction. The lock portion 7 locks the lever 5 in the connected position.
In this breaker device, when an incompletely-connected condition is encountered, the lever 5 is forcibly displaced in the disconnecting direction by the bias of the torsion coil spring 6, thereby preventing the fixed electrodes 2 and 3 from being kept in the incompletely-connected condition. When the two electrodes 2 and 3 are properly connected together, the lever 5 is retained by the lock portion 7, and therefore is held in the connected position against the bias of the torsion coil spring 6, thereby locking the two fixed electrodes 2 and 3 in the properly-connected condition.
In the above known breaker device, the torsion coil spring 6 is used as means for urging the lever 5 in the disconnecting direction. One arm 6A of this spring extends along and is held against a lower surface of the housing 1, while the other arm 6b is engaged with the lever 5 along the length of this lever.
This torsion coil spring 6 is resiliently deformed or bent in such a manner that the angle between the two arms 6A and 6B is reduced, and the lever 5 is urged in the disconnecting direction by a resilient restoring force thereof.
The amount of resilient bending of the torsion coil spring 6 (i.e., the urging force in the disconnecting direction) gradually increases as the lever 5 is tilted in the connecting direction. When the lever 5 is locked in the proper connected position, the amount of resilient bending of the torsion coil spring 6 (i.e., the urging force) is at a maximum. The breaker device is usually kept locked in the properly-connected condition. Therefore, a condition in which the torsion coil spring 6 is much resiliently bent, and a condition in which a large stress is exerted on the lock portion 7 and the lever 5 by the bias of the torsion coil spring 6, lasts a long time. As a result, there are possibilities that the torsion coil spring 6 has a permanent set in fatigue and that a creep develops in the lock portion 7 or the lever 5.
Further, the breaker device is usually kept locked in the properly-connected condition, and therefore the lock portion 7 needs to have sufficient strength to lock the lever 5 in the connected position against the bias of the torsion coil spring 6. This required strength results in a drawback in that the lock portion 7 must have a large size. Another problem is that when the locking position is released due to an impact or vibration, the lever 5 is accidentally moved in the disconnecting direction by the bias of the torsion coil spring 6, so that the fixed electrodes 2 and 3 are disconnected from each other.